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Induction and removal of inward‐going rectification in sheep cardiac Purkinje fibres
Author(s) -
Carmeliet E.
Publication year - 1982
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1982.sp014232
Subject(s) - conductance , membrane potential , resting potential , depolarization , chemistry , voltage clamp , biophysics , clamp , electrophysiology , reversal potential , purkinje fibers , patch clamp , medicine , physics , biology , biochemistry , mechanical engineering , clamping , engineering , condensed matter physics
1. In sheep cardiac Purkinje fibres superfused with K‐free, Na‐free medium, the membrane potential can be stable either at a low negative level (‐50 mV) or at a high negative level (‐100 mV). The mechanism underlying the existence of these two stable potential levels was investigated using the two‐micro‐electrode voltage‐clamp technique. 2. By applying a voltage clamp of a certain duration at an appropriate level the membrane potential could be shifted from one stable level to the other. The shift was observed in Cl‐free medium, excluding a redistribution of Cl as a possible explanation. 3. Currents during and following a voltage step and their change with amplitude and duration of the voltage step could not be explained on the basis of depletion or accumulation of K ions in the narrow extracellular clefts. 4. Instantaneous currents determined from the high negative resting level showed a high conductance and a pronounced inward rectification, while measurements from the low negative resting level indicated a low conductance and absence of inward rectification. The steady‐state current—voltage relation was dependent on the holding potential and showed memory or hysteresis. 5. Estimation of the conductance by superimposed short voltage‐clamp pulses showed an increase in conductance during a hyperpolarizing clamp from the low negative level and a decrease in conductance during a depolarizing clamp from the high negative level. The time‐dependent current during a hyperpolarizing clamp from the low negative level reversed direction at a potential level corresponding to E K , assuming a cleft K concentration of about 1 mM. In the presence of 0·1 mM‐Ba the time‐dependent current was abolished. 6. The results suggest that the shift between the two stable levels is due to a time‐dependent conductance change in the K inward rectifier channel, i K1 . The existence of memory excludes activation or de‐activation only depending on the voltage gradient. Interaction of extracellular K ions with a site in the membrane is proposed as the activating mechanism.